By some accounts, human beings have been aging distilled spirits in wooden containers for almost five hundred years. Despite billions of person-hours of experience, the myriad of chemical reactions responsible for the flavor of wood-aged spirits are not fully understood. Spirits derive their distinct characteristics over time while stored in wooden containers in part by the production and presence of esters. Esters are compounds made by chemically bonding acid molecules and alcohol molecules to form new compounds, often with pleasant aromas and tastes. This process is known as “esterification.” In addition to esterification, wood-aged spirits derive additional characteristics through other processes, including extraction of flavor compounds from the wood container (e.g., the ubiquitous oak barrel). These processes are not necessarily separate or distinct, and can interact with and affect each other.
Spirits also derive their distinct characteristics over time while stored in wooden containers in part from the quicker evaporation of more volatile organic compounds (VOCs) through the barrel walls, over the slower evaporation of other organic compounds. The aging process thus eliminates some undesired compounds, such as methanol, and concentrates and rebalances others, such as flavorful esters formed from reactions with the wood barrel.
Attempts have been made to accelerate maturation of distilled spirits by cycling or varying pressures over relatively large ranges (e.g., between −2 and 10 ATM; see U.S. Patent Publication No. 2013/0149423). These processes generally do not yield a product close enough to that produced by traditional means. Other environmental conditions are more important to achieve characteristics associated with a mature flavor.
Consumers of distilled spirits are often educated and discerning. Many will refuse to consume or pay a premium for non-authentic tasting products. What is needed is a means by which the quality and complexities associated with traditionally aged spirits can be achieved in a significantly reduced timeframe, sometimes with a reduction in the evaporation of finished goods and a reduction of the build-up of ethyl acetate.